Effect of Food Components on Growth of Escherichia coli O157

1982年，O157大肠埃希氏菌首次被确认为致病原因。牛产品最常与食源性感染E.ColiO157有关。然而，最近的暴发表明，其他食物类型也可能是这种病原体的传播媒介。据报道，O157大肠杆菌菌株对低pH值和低水活度具有耐受性。特别是，耐酸性是E.ColiO157的重要特性，因为E.ColiO157必须通过酸性胃屏障才能引起胃肠道疾病。大肠杆菌O157细胞的耐酸性取决于它们的生长条件。为阐明该病原菌感染的原因，对O157菌株在食品中的存活和生长情况进行了调查。研究了O157菌株在食品中产生维罗毒素的情况，结果表明，O157菌株对酱油具有较高的耐受性。用12.5%酱油培养的O157菌株生长良好，但活的非致病性大肠杆菌数量减少。当O157菌株接种在含有14%酱油的LB琼脂上时，3株大肠杆菌O157：H7都能形成可见的菌落，但3株非致病的大肠杆菌都不能形成可见的菌落。当大肠杆菌细胞与各种香料的乙醇溶解部分孵育时，大肠杆菌O157菌株在肉豆蔻乙醇溶解部分中的存活率较低。在相同的条件下，非致病性大肠埃希氏菌的数量没有减少。肉豆蔻提取物对E.ColiO157的特异性杀菌效果较好。蔬菜中的E.ColiO157的耐酸性低于EC培养基中的细胞，EC培养的E.ColiO157产生的vero毒素明显高于蔬菜提取物中的verooxin。这表明，蔬菜中的某些成分可能会阻止O157大肠杆菌产生维罗毒素。

Escherichia coli O157 was first recognized as a cause of illness in 1982. Bovine products have most often been implicated in food-borne infections with E.coli O157. However recent outbreaks indicate that other food types may also serve as vehicles of transmission for this pathogen. E.coli O157 strains are reported to be tolerant to low pH and low water activity. In particular, the acid tolerance is important property of E.coli O157 because E.coli O157 must pass through the acidic gastric barrier to cause gastrointestinal disease. Acid resistance of E.coli O157 cells depends on their growth conditions. To clarify the reason for the infection of this pathogen, the survival and growth of E.coli O157 in foods were investigated. The productin of verotoxin by E.coli O157 in foods was also investigated.When E.coli O157 : H7 was incubated with the various seasonings, the O157 strains showed a high tolerance to soy sauce. E.coli O157 strains incubated with 12.5% soy sauce grew well, but the viable non-pathogenic E.coli populations were reduced. When the O157 strains were inoculated on LB agar media containing 14% soy sauce, all three E.coli O157 : H7 strains formed visible colonies, but all three non-pathogenic E.coli strains could not form visible colonies.When the E.coli cells were incubated with ethanol-soluble fractions of various spices, the E.coli O157 strains showed lower survival ratios in an ethanol-soluble fraction of nutmeg. The population of non-pathogenic E.coli was not reduced under the same conditions. The nutmeg extract may be useful for specific sterilization of E.coli O157.The acid resistance of E.coli O157 grown in vegetables was found to be low in comparison with that of the cells grown in EC medium.The production of verotoxin in E.coli O157 grown in EC medium was clearly higher than that of verotoxin in E.coli O157 grown in vegetable extracts. This suggest that some components of vegetables might prevent E.coli O157 from producing verotoxin.